// Quantum Computing
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Suppose I have an $n$ -qubit pure state $|\psi\rangle$ that I can prepare using a unitary $U$ s.t. $U|0\rangle = |\psi\rangle$ . I would like to determine whether the first qubit in the system is unen…

is it true (H⊗H)CZ(H⊗H) = CNOT?, I have calculated it but did not get the right result. But people said that the result of the operation is the CNOT gate.

I often see the papers saying that a T gate can be implemented by preparing a magic state and using gate teleportation (1-bit teleportation) as shown in the first figure below. On the other hand, I al…

I'm looking for open-source code that implements lattice surgery merging and splitting between two rotated surface code logical qubits in STIM (for d=3 or above). Whilst there are some excellent expla…

I want to know how to solve a 01 Knapsack problem (or any optimization problem) on real Quantum Hardware only. I don't want to use an Application class or any classical simulation technique. If anyone…

As was already asked about in this phys.SE question many years ago—which, sadly, got closed and never received an answer—is there a collection of counterexamples in quantum information theory, "in the…

I want to solve QUBO with non-zero diagonal elements in matrix Q using QAOA. But I want to solve for a large enough problem size (30+ variables) and hence want to divide my circuit into subcircuits. C…

I am interested in using the D-Wave CQM hybrid solver for solving the job shop problem. I would like to get more information about the internal working of this solver but I have been unable to find mo…

A QRAC encodes $n$ bits in $m$ qubits so that one of the bits can be retrieved. Let $p>0.5$ be the success probability of the receiver correctly obtaining any one of the $n$ bits of their choice by pe…

I'm using Qiskit 1.0.0. I'm trying to define a custom gate from a certain wavefunction and insert it in a quantum circuit that I want to run and measure the counts. The relevant code for the question …

I would like to ask about the need of a low temperature for the operation of superconducting qubits. I know a superconducting qubit is made from basically a LC circuit and Josephson junction. So obvio…

I want to understand in some detail why superconducting qubits need periodic calibration. The usual, hand wavy explanation is environmental effects that tend to vary. However, I suspect that the actua…

This question may be slightly opinion based, so I apologise if this is the incorrect place to ask. My question is, is there any use for Shor's integer factorisation algorithm other than for breaking p…

Basis is for this post ist the paper https://arxiv.org/pdf/1902.00445.pdf I want to do something similar using graph data encoded in quantum states. The circuit structure should look like this (first …

On qiskit, I have defined a QUBO, called qp as follows: print(qp.prettyprint()) Minimize -1.7324559764718837*x10^2 + 0.00619189721450626*x10*x11 ... + 3.6972673229589947*x27*x29 - 32.42658793825545*x2…

I read about single-shot error correction using 3D gauge color codes. I saw the claim that it enables significant qubit and time overhead improvement regarding 2D surface codes, since it does not requ…

Suppose that we have this kind of circuit where the first unitary operator U is used for the state preparation while the Hadamard operator is used of state detection. Let's say we try to run this circ…

Define the single qubit Clifford hierarchy recursively by $ \mathcal{C}^1:=<iX,iZ> $ (the determinaint 1 subgroup of the Pauli group) as well as $$ \mathcal{C}^k:=\{ V \in \mathsf{SU}(2): VpV^{-1} \te…

Sorry if this question sounds trivial, however I'm struggling to get the intuition of how quantum circuits are actually run on real quantum hardware. As far as I know, in a simulated environment, circ…

I am curious about what are quantum computers actually doing today. I seem to only be able to find information online about what they could be used for in the future (i.e. breaking encryption, quantum…

I have read Fujitsu's white paper for a brief introduction to their device: http://marketing.us.fujitsu.com/rs/407-MTR-501/images/quantum-inspired-computing.pdf As far as I know, Fujitsu's hardware is…

What is the need to apply the Hadamard gate as the first step while designing the diffuser circuit in the implementation of Grover's algorithm? I know what the gate does but I cannot understand what s…

I wasn't quite sure where to post this as I don't know if this is a Qiskit specific thing or not, but I'm not sure how to interpret this result I got from running a simulation. from result.data(): {'c…

I want to use historical data for 5 stocks from YahooFinance and then calculate mean vector and covariance matrices, so I can optimize them with QAOA. Anyone know what is wrong with this code: num_ass…